Because of the common association between the binding sites of the NF-1 and AP-1 transcription factors in the regulatory region of a number of genes, we call the adjacent binding sites for these two factors the "glial neurobox". It has been suggested that the NF-1 site in the JCV regulatory region is required for both JCV early transcription and DNA replication. Because of the possible involvement of NF-1 with the expression of JCV and other genes expressed in the CNS/PNS, we have screened cDNA libraries prepared from neonatal and fetal brain tissue for the possible presence of a brain specific NF-1 factor with an oligonucleotide probe homologous with the DNA binding domain of the NF-1 cDNA clone reported from HeLa cells. A number of cDNA clones were isolated from both cDNA libraries. Two of the clones from the neonatal brain library and one clone from the fetal brain library were sequenced. The 3 sequenced cDNA clones were homologous with each other, except for a few bases at the 5' end of the two longest clones and a 150-bp insertion in the 3'-region of the shortest clone. The DNA binding region located at the 5' -end of the clones was highly conserved between the brain clones and that reported for the HeLa NF-1 clone. On the other hand, the 3'-region of the cDNA clones isolated from the brain libraries were highly homologous but differed from that reported from HeLa cells. The 3'-region of NF-1 molecules were reported to contain the transcriptional activational domain of the molecule. One of the brain cDNA clones was cloned into a T7 RNA polymerase expression vector, and a specific size protein was over-produced on induction of expression with IPTG. An extract prepared from cells overproducing the specific protein was demonstrated to contain a specific binding activity with an NF-1 oligonucleotide. In order to determine if expression of other classes if the NF-1 family could be detected in primary fetal brain cells. RT-PCR analysis was performed with poly A-selected RNA from primary fetal cells and HeLa cells. With the use of class-specific primers the expression of at least four classes of the NF-1 protein family could be detected in both the brain and the HeLa cell lines. Similar studies were performed with the class specific primers with RNA extracted from B-cell lines, however, without the detection of any PCR products. These results suggest that the expression of processing of NF-1 genes(s) in B-cells is different than that in the brain and HeLa cell lines, since specific NF-1 binding activity was detected by both competitive binding and DNase 1 protection assays with extracts prepared from B-cells.